What’s the weirdest thing you learned this week? Well, whatever it is, we promise you’ll have an even weirder answer if you listen to PopSci’s hit podcast. The Weirdest Thing I Learned This Week hits Spotify, YouTube, Apple, and everywhere else you listen to podcasts every-other Wednesday morning. It’s your new favorite source for the strangest science-adjacent facts, figures, and Wikipedia spirals the editors of Popular Science can muster. If you like the stories in this post, we guarantee you’ll love the show.

FACT: We really have no idea why humans kiss 

By Rachel Feltman

This year’s Ig Nobel Prize in biomechanics went to researchers trying to answer a surprisingly complicated question: what’s a kiss? Their definition—”non-agonistic interactions involving directed, intraspecific, oral-oral contact with some movement of the lips/mouthparts and no food transfer”—was concocted to exclude such exchanges as ants feeding each other with their mouths, bees and birds vomiting at one another, and fish that fight by smashing their open jaws together. 

Defining a kiss might seem like a silly scientific endeavor, but it was a crucial first step for their research. Once they had definite criteria for a kiss in place, they went looking for that specific behavior in research about all sorts of primates. By mapping the appearance of kissing the same way they might map any other evolutionary adaptation, they came up with an estimation of how far back the trait could have evolved. The number they landed on is some 20+ million years. 

Listen to this week’s episode to hear more about the 2026 Ig Nobel winners, and to learn why kissing is such a mysterious—and unique—human behavior. 

FACT: The “American cheetah” wasn’t a cheetah at all 

Featuring Riley Black

This week’s episode features special guest Riley Black. Her new book, Tyrant Lizard Queen: The Love, Life, and Terror of Earth’s Greatest Carnivore, comes out later this month. 

For her guest spot on this week’s Weirdest Thing, Riley decided to tell us all about the fastest—and perhaps fattest—cat in North America. 

For decades, paleontologists thought that an extinct cat called Miracinonyx evolved into a cheetah-like springer specifically to chase down North America’s speedy pronghorns. It was a tidy, romantic story of predator and prey evolving together in lockstep until one had gone extinct; it explained why pronghorns were so dang fast, too. But Riley always found the story a little fishy, and she wasn’t the only one: in 2023, researchers noted that these American cats had forearm bones more suited for grasping prey (cougar-style) than for running super fast (like a cheetah). 

New research has put another nail in the coffin of the “American cheetah.” For starters, their fossils were found as far north as the Yukon—where they wouldn’t have had any pronghorns to hunt. And based on their DNA, the researchers say, they’re much more closely related to modern pumas. They also had a unique diet: according to isotope analysis, the researchers think the Yukon-dwelling cats feasted on salmon. That leaves us with one big question: what were pronghorns running from?

FACT: Rich people love building little stone houses for themselves (to be dead in)

Featuring Amanda Reed

Old friend-of-the-pod Amanda came back to join us this week. She took us on a tour of mausoleum history. 

Walk into Pittsburgh’s Allegheny Cemetery, and you’ll find it hard to miss the sphinxes. They’ve got ample bosoms, appropriative headdresses, and nothing whatsoever to do with actual Egyptian funeral traditions. They’re actually monuments to the fortune (and ego) of the late industrialist Emil Winter. 

Emil, who got to move into these fancy digs in 1941, was not unique in desiring such an opulent postmortem dwelling. In fact, he decided to have it built after seeing a similar one by the same architect: the Woolworth family mausoleum in New York City. 

Listen to this week’s episode to learn more about humanity’s enduring desire to build fancy houses for the deceased. 

The post Why did kissing evolve? If we want to find out, we’ve got to decide what counts as a kiss first.  appeared first on Popular Science.

What’s the weirdest thing you learned this week? Well, whatever it is, we promise you’ll have an even weirder answer if you listen to PopSci’s hit podcast. The Weirdest Thing I Learned This Week hits Spotify, YouTube, Apple, and everywhere else you listen to podcasts every-other Wednesday morning. It’s your new favorite source for the strangest science-adjacent facts, figures, and Wikipedia spirals the editors of Popular Science can muster. If you like the stories in this post, we guarantee you’ll love the show.

FACT: Hector the tickle robot is real, and they’re spectacular 

By Rachel Feltman

Have you ever wondered why humans are so ticklish? While many animals experience a type of tickle known as knismesis—a sort of moving itch caused by motion against your skin—the laugh-out-loud sensation called gargalesis is way less common. It’s a phenomenon that’s pretty unique to primates (though it’s possible that rats are a bit ticklish as well). And while there are plenty of theories, no one has a great explanation for why this ticklishness evolved—or at least not one that would be easy to confirm.

But while the origins and purposes of gargalesis remain mysterious, that hasn’t stopped scientists from studying how tickling works. In one recent study scientists surveyed adults from several distinct cultures to see how they felt about tickling. The results were surprisingly universal. Participants from The Netherlands, Greece and China gave comparable answers about their history of tickling and being tickled and reported being ticklish in the same locations. That hints at a deep evolutionary origin for this sensation (and our feelings about it). 

This most recent study relied on survey data, but other research projects have tried to take a more quantitative look at tickles. That’s where Hector the tickle robot comes in. He’s designed to deliver a perfectly-calibrated foot tickle on command, allowing scientists to track exactly what physiological changes occur post-tickle and exactly when they kick in. He’s also helping scientists understand why we can’t tickle ourselves—and how that can help us survive unwanted tickling from others. Listen to this week’s episode to learn more!

FACT: How prickly ash and chili pepper combine to create a fascinating taste explosion 

Featuring Priya Mani

This week’s episode features special guest Priya Mani. She’s a food historian, award-winning writer, and a designer who leads research-driven projects on ingredients and flavor. She joined us this week to share some facts from her upcoming book, “Spiced: Recipes Celebrating Spices from Around the World.” You can preorder it now! 

Priya took us on a historical, culinary and scientific journey to explain why sichuan peppercorns (and other berries from various species of prickly ash) make your mouth buzz instead of burn. It all comes down to a compound called sanshool. 

When you eat food that’s spicy—think a hot chili pepper—the compound called capsaicin binds to the same receptors in your skin that are stimulated by actual heat. WHen these TRPV1 receptors get activated, they signal to your brain that something dangerously hot is touching you. 

You might associate szechuan peppercorns and other kinds of prickly ash berries with spicy food, but these fruits don’t actually contain any of the aforementioned capsaicin—so they don’t trick your brain into sensing heat. Sanshool can trick your brain in an entirely different way by acting on potassium channels, which are tiny pores that let potassium flow out of your nerve cells. By giving positively-charged potassium ions an easy exit, nerve cells are able to maintain a slightly-negative charge that keeps them from randomly firing.

Sanshool manages to block one of those potassium channels, which means positive charge starts to build and the nerve cell gets closer and closer to firing. The result is a hyperactive neuron that starts stuttering out little bursts of irregular signals. Your brain does the best it can to interpret that information, and the result is a sense that something is literally buzzing inside your mouth. 

That’s why dishes that combine prickly ash berries with chili peppers are infamous for creating a culinary sensation like no other: your brain is basically telling you that there’s a hot bee bouncing around your mouth. And gosh, that fiery insect is delicious. 

You can find more of Priya’s fantastic food science on Instagram.

FACT: These shark have teeth in their eyeballs

By Laura Baisas, News Editor and co-host of Popular Science’s Ask Us Anything podcast

While interviewing marine biologist, Jaida Elcock (@sofishtication_) an MIT and Woods Hole Oceanographic Institution (WHOI) PhD candidate and ace whale shark-tagger, she told me that whale sharks have teeth on their eyeballs. This sounded insanely painful to me, so I had to know more. 

Whale sharks (Rhincodon typus) are the biggest fish in the world. While their maximum size is still a mystery, they can grow as large as 60 feet and weigh about 11 tons. In addition to that girth, they really do have tiny teeth covering their eyeballs called dermal denticles. Dermal denticles themselves are found on several shark species and they cover their bodies like scales. They are small, V-shaped pieces and decrease drag and turbulence as they swim. While dermal denticles do help sharks swim faster, they also provide some defence against any other sharks that might try to take a bite of them

The dermal denticles on whale shark’s eyeballs, also called eye-teeth, likely help shield their eyes from the elements. A team in Japan first detailed this in a study published in 2020 in the journal PLOS One. They studied the eyes of both living and dead whale sharks and saw that a single whale shark eyeball could have over 3,000 dermal denticles around the eyes. They are also clustered around the iris.

Most sharks have poor eyesight, so much protection around their eyeballs means that their eyesight is likely pretty important for whale sharks. Evolution is cool. 

The post Yes, scientists really built a “tickle robot.” Here’s why. appeared first on Popular Science.